U.S. patent number 5,834,689 [Application Number 08/162,430] was granted by the patent office on 1998-11-10 for cubic boron nitride composite structure.
This patent grant is currently assigned to PCC Composites, Inc.. Invention is credited to Arnold J. Cook.
United States Patent |
5,834,689 |
Cook |
November 10, 1998 |
Cubic boron nitride composite structure
Abstract
The present invention pertains to a composite structure
comprised of a matrix material, such as metal, and a plurality of
cubic boron nitride particles dispersed within and surrounded by
the matrix material. In a first embodiment, the composite structure
is used as an electronic package to house an electrical device such
as an integrated chip. The cubic boron nitride particles are
dispersed within the matrix material in proportion such that the
coefficient of thermal expansion of the package essentially matches
that of the electronic devices. In another embodiment, the
composite structure can be used as a thermal conductor, such as a
heat sink. Since cubic boron nitride particles have the highest
thermal conductivity of any ceramic, they act in combination with
the matrix metal to transfer heat efficiently. In another
embodiment, the composite structure can be used as a component
subject to attrition. The cubic boron nitrides offer unexcelled
wear resistance and transfer the heat efficiently.
Inventors: |
Cook; Arnold J. (Mt. Pleasant,
PA) |
Assignee: |
PCC Composites, Inc. (Longmont,
CO)
|
Family
ID: |
22585589 |
Appl.
No.: |
08/162,430 |
Filed: |
December 2, 1993 |
Current U.S.
Class: |
174/50;
257/E23.006; 257/E23.112 |
Current CPC
Class: |
H01L
23/3733 (20130101); H05K 7/20481 (20130101); H01L
23/142 (20130101); H02G 3/08 (20130101); H01L
2924/0002 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
23/12 (20060101); H01L 23/34 (20060101); H05K
7/20 (20060101); H01L 23/14 (20060101); H01L
23/373 (20060101); H02G 3/08 (20060101); H02G
003/08 (); H05K 005/02 () |
Field of
Search: |
;174/50 ;428/328 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kincaid; Kristine L.
Assistant Examiner: Reichard; Dean A.
Attorney, Agent or Firm: Klarquist Sparkman Campbell Leigh
& Whinston, LLP
Claims
What is claimed is:
1. A net shape composite article comprising:
a metal matrix material; and
a plurality of cubic boron nitride particles dispersed within and
surrounded by the metal matrix material.
2. A composite article as described in claim 1 wherein the
composite article has an outer skin consisting essentially of a
metal which forms a continuum with the metal matrix and which is of
the same composition as the metal matrix.
3. A composite article as described in claim 1, including particles
of material besides the cubic boron nitride particles.
4. A composite article as described in claim 3 including
reinforcement fibers dispersed within the metal matrix
material.
5. A package for housing an electronic device comprising:
a metal matrix material; and
a plurality of cubic boron nitride particles dispersed within the
metal matrix material in proportion such that the coefficient of
thermal expansion of the package essentially matches that of the
electronic device.
6. A package as described in claim 5 wherein the package has an
outer skin comprised of pure matrix material.
7. A package as described in claim 5 including particles of
material besides the cubic boron nitride particles.
8. A package as described in claim 7 including reinforcement fibers
dispersed within the matrix material.
9. A package as described in claim 8 which is net shaped.
10. A net shape thermally conductive body comprising:
a metal matrix material; and
a plurality of cubic boron nitride particles dispersed within and
surrounded by the metal matrix material.
11. A thermally conductive body as described in claim 10 wherein
the matrix material forms heat transfer fins.
12. A thermally conductive body as described in claim 10 including
particles of material besides the cubic boron nitride
particles.
13. A thermally conductive body as described in claim 12 including
reinforcement fibers disposed within the matrix material.
14. A thermally conductive body as described in claim 10 wherein
the matrix material comprises aluminum.
15. A thermally conductive body as described in claim 10 wherein
the matrix material comprises magnesium.
16. A thermally conductive body as described in claim 10 wherein
the matrix material comprises copper.
17. A thermally conductive body as described in claim 10 wherein
the matrix material comprises a non-ferrous metal.
18. A thermally conductive body as described in claim 10 wherein
the matrix material comprises a ferrous metal.
19. A thermally conductive body as described in claim 15, further
comprising an outer skin consisting essentially of a metal which
forms a continuum with the metal matrix and which is of the same
composition as the metal matrix.
20. A net shape component subject to wear comprising:
a metal matrix material; and
a plurality of cubic boron nitride particles dispersed within and
surrounded by the metal matrix material.
21. A component as described in claim 20 wherein the matrix
material has a reinforced portion in which the cubic boron nitride
particles are disposed and an unreinforced portion which is void of
cubic boron nitride particles.
22. A component as described in claim 21 including particles of
material besides the cubic boron nitride particles.
23. A component as described in claim 22 including reinforcement
fibers dispersed within the matrix material.
24. A net shape composite structure comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the matrix material;
particles of material besides the cubic boron nitride particles
dispersed within and surrounded by the matrix material; and
an outer skin comprised of pure matrix material.
25. A thermal conductor comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the matrix material; and
heat transfer fins formed by the metal matrix material.
26. A net shape thermal conductor comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the matrix material; and
particles of material besides the cubic boron nitride particles
dispersed within and surrounded by the matrix material.
27. A net shape component subject to wear comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the matrix material;
particles of material besides the cubic boron nitride particles
dispersed within and surrounded by the metal matrix material;
and
an outer skin comprised of pure matrix material.
28. A composite article comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the metal matrix material; and
reinforcement fibers dispersed within the metal matrix
material.
29. A thermally conductive body comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the metal matrix material; and
reinforcement fibers dispersed within the metal matrix
material.
30. A component subject to wear comprising:
a metal matrix material;
a plurality of cubic boron nitride particles dispersed within and
surrounded by the metal matrix material; and
reinforcement fibers dispersed within the metal matrix material.
Description
FIELD OF THE INVENTION
The present invention is related to composite materials. More
specifically, the present invention is related to a composite
material having cubic boron nitride.
BACKGROUND OF THE INVENTION
It is known to add reinforcement particles to a material to
increase the strength and wear resistance of a material.
Reinforcement particles are typically made of ceramic particles or
graphite particles. Though these particles such as SiC do offer
increased strength and wear resistance, they suffer in that they
provide only limited heat transfer increases and limited control of
thermal expansion.
Accordingly, the present invention describes a composite material
and components such as electronic packages which use cubic boron
nitride to provide high wear resistance and the highest heat
transfer and CTE in a composite system. Also, proposed is the
method of net shape production with a pure metal skin with pressure
infiltration casting. Diamond has a thermal conductivity as high as
2,000 WM/.degree.C. followed by cubic boron nitride with a
conductivity as high as 1,700 WM/.degree.C. However, cubic boron
nitride often creates a higher thermal conductivity composite
material and component.
SUMMARY OF THE INVENTION
The present invention pertains to a composite structure comprised
of a matrix material, such as metal, and a plurality of cubic boron
nitride particles dispersed within and surrounded by the matrix
material.
In a first embodiment, the composite structure is used as an
electronic package to house an electrical device such as an
integrated chip. The cubic boron nitride particles are dispersed
within the matrix material in proportion such that the coefficient
of thermal expansion of the package essentially matches that of the
electronic devices. Cubic boron nitride is more stable than diamond
at high temperature. At temperatures near 800.degree. to
900.degree. C. diamond starts to change from a high thermally
conductive form of carbon to a very low form. Diamond is also more
reactive with some liquid metals such as aluminum. Composite
components made by liquid metal processes such as pressure casting
require high temperatures of the particles to be infiltrated. Cubic
boron nitride reinforced composites are higher in thermal
conductivity than diamond reinforced composites due to the
interface between the metal and particles even though diamond has a
higher thermal conductivity.
In another embodiment, the composite structure can be used as a
thermal conductor, such as a heat sink. Since cubic boron nitride
particles have high thermal conductivity, they act in combination
with the matrix metal to transfer heat efficiently.
In another embodiment, the composite structure can be used as a
component subject to attrition. The cubic boron nitride particles
offer unexcelled wear resistance and transfer the heat
efficiently.
The invention is also a method of producing a cubic boron nitride
composite structure comprising the steps of casting cubic boron
nitride particles, binding particle and flow medium into a mold.
Then, there is the step of heating the mixture such that flow
medium is essentially removed and the binding particles hold the
cubic boron nitride particles into a preform. Next, there is the
step of infiltrating the preform with molten matrix material. Then,
there is the step of cooling the matrix material. Alternatively,
loose cubic boron nitride particles may be infiltrated directly
with the matrix material.
In an alternative embodiment, the method for producing a composite
structure includes the step of casting a mixture of cubic boron
nitride particles and matrix material in a mold. Then, there is the
step of cooling the mixture such that the matrix material
solidifies. Preferably, the cooling step includes the step of
directionally solidifying the matrix material.
In an alternative embodiment, the method for producing a composite
structure includes the steps of mixing cubic boron nitride
particles and metal particles and then pressing or forming them
into a shape and then sintering until solid.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, the preferred embodiment of the
invention and preferred methods of practicing the invention are
illustrated in which:
FIG. 1 is a schematic representation showing a cross section of the
composite structure.
FIG. 2 is a schematic representation showing a cubic boron nitride
composite electronic package.
FIG. 3 is a schematic representation showing a cubic boron nitride
composite thermal transfer element.
FIG. 4 is a schematic representation showing a cubic boron nitride
composite brake rotor.
FIG. 5 is a schematic representation showing a cross section of the
brake rotor.
FIG. 6 is a schematic representation showing a cubic boron nitride
composite bearing.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like reference numerals refer
to similar or identical parts throughout the several views, and
more specifically to FIG. 1 thereof, there is shown a composite
structure 10. The structure 10 is comprised of a matrix material
12, such as metal, and a plurality of cubic boron nitride particles
14 dispersed within and surrounded by the matrix material 12.
Preferably, the composite structure 10 also has reinforcing fibers
15 dispersed within the matrix material 12, which can reduce the
amount of cubic boron nitride required. A skin 18 of pure matrix
material can surround the composite structure. In this embodiment,
all cubic boron nitride particles 14 are disposed completely below
the surface of the composite structure 10. Alternatively, some of
the cubic boron nitride particles 14 can be disposed on the outer
surface of the composite structure 10. The matrix material is
preferably metal such as aluminum, copper, magnesium, nickel or
silver, but is not limited to these.
As shown in FIG. 2, the composite structure 10 can be a package 16
for housing an electrical device 18, such as a computer chip. The
cubic boron nitride particles 14 are dispersed within the matrix
material 12 in proportion such that the coefficient of thermal
expansion of the package 16 essentially matches that of the
electronic device 18. The cubic boron nitride composite packages 16
can be manufactured to match the coefficient of thermal expansion
of silicon, alumina or gallium arsenide circuit substrates. In this
manner, during thermal cycling, the package 16 and the electronic
device 18 will expand and contract in unison thereby preventing
separation of the electronic device 18 from the package 16 which
would result in an electronic disconnection. This is very important
in applications where a wide range of temperatures exist such as in
satellites and high speed aircraft. The package 16 preferably has
unreinforced areas 20 of pure matrix material 12 for drilling
operations or for welding or brazing procedures. Further, the cubic
boron nitride particles 14 transfer heat extremely well. The
thermal conductivity of this system can be higher than any other
composite system. 1100 aluminum and 70% cubic boron nitride
particles produce a conductivity 50-100% greater than that of
SiC/Al.
As shown in FIG. 3, the composite structure 10 can be used a
thermal conductor, such as a heat sink 22 for an electronic device
18. Preferably, the heat sink 22 has heat transfer fins 24 and is
comprised of a highly conductive matrix material such as aluminum.
The cubic boron nitride particles have a thermal conductivity of
1700-1750 W/M.degree.C. which is the highest thermal conductivity
of any ceramic. Accordingly, a composite heat sink 22 having cubic
boron nitride particulates would transfer heat more efficiently
than a composite heat sink having graphite or silicon carbide
particles. Preferably, the heat sink can draw heat away from a
plurality of electronic devices 18 as shown by the dotted lines.
Preferably, the heat sink 22 has cooling channels for transferring
heat away. Alternatively, a heat pipe can be included to add heat
to the composite structure 10.
The composite structure can be a component which is subject to wear
such as a brake rotor 26, as shown in FIG. 4, or a bearing 40, as
shown in FIG. 6. The cubic boron nitride particles 14 offer
unequaled wear resistance and transfer heat efficiently. For
economy, cubic boron nitride particles 14 can be selectively used
where wear resistance is most desired. Other types of particles
such as silicon carbide fibers or graphite can also be used in
combination with the cubic boron nitride. Preferably, as shown in
FIG. 5, which is a cross section of the brake rotor shown in FIG.
4, the matrix material 12 has a reinforced portion 30 in which the
cubic boron nitride particles 14 are disposed and an unreinforced
portion 20 which is void of cubic boron nitride particles 14. In
this manner, the cubic boron nitride particles 14 can be positioned
only in wear areas. This selective positioning can be attained by
forming the cubic boron nitride particles 14 into a preform which
is then infiltrated with molten matrix material 12. The surface of
the metal matrix can be etched away to expose the cubic boron
nitride particles. Cubic boron nitride composite brake shoes are
also envisioned as well as almost any structure which is subject to
attrition.
The invention is also a method of producing a cubic boron nitride
composite structure comprising the steps of casting cubic boron
nitride particles and flow medium into a mold. Then, there is the
step of heating the mixture such that flow medium is essentially
removed. Next, there is the step of infiltrating the preform with
molten matrix material. Then, there is the step of cooling the
matrix material. Rapid cooling can keep reactions to a minimum
between the cubic boron nitride and metal. Preferably, binding
particles are disposed within the flow medium and during the
heating step the binding particles are sintered together to hold
the cubic boron nitride particles in a preform. Loose cubic boron
nitride particles may also be infiltrated. Other processes may be
used but they may require a coating on the cubic boron nitride to
prevent reaction.
Preferably, the cooling step includes the step of directionally
solidifying the matrix material and the cubic boron nitride
particles. If it is desired, the preform can be evacuated prior to
heating or infiltration.
In an alternative embodiment, the method for producing a composite
structure includes the step of casting a mixture of cubic boron
nitride particles and matrix material in a mold. Then, there is the
step of cooling the mixture such that the matrix material
solidifies. Preferably, the cooling step includes the step of
directionally solidifying the matrix material.
An alternative method includes the steps of forming a preform of
cubic boron nitride and then loading it into a mold, pulling a
vacuum and then forcing liquid metal into the mold with gas or
mechanical pressure.
In the operation of the preferred embodiment, an electronic radar
module for an aircraft is produced by mixing 50% by volume 100
micron size cubic boron nitride particles 14 with 25% by volume 10
micron cubic boron nitride particles 14 with 2% by volume 1 micron
silica particles and wax to form a preform mixture. The preform
mixture is then cast into a mold and heated at a controlled rate to
over 700.degree. C. so that the wax is essentially removed and the
silica particles become fused and bind the cubic boron nitride
particles 14 together to form a preform. The preform is then
positioned within a mold and infiltrated with molten aluminum. It
is not necessary for the preform to fill the entire volume of the
mold. Also, cubic boron nitride packing over 50% may not require
silica particles. Open areas within the preform will be filled with
pure aluminum to form unreinforced portions 20 on the package 16.
By the use of pressure infiltration casting, a thin skin of metal
can be formed around the part such that the part can be net shape
and easily plated on the pure metal surface. This makes it possible
for the user to drill out unreinforced areas left in the preform
for feedthroughs, etc. and the user never needs to machine the
cubic boron nitride composite material.
The cast package 16 is then directionally solidified and removed
from the mold. The resulting coefficient of thermal expansion of
the radar module matches that of the gallium arsenide circuits.
Holes are drilled in the unreinforced portions 20. Wire
feedthroughs 34 are inserted into the holes and hermetically sealed
by brazing. Gallium arsenide circuits are brazed on the radar
module. The entire radar module is then connected to the
appropriate apparatuses within the aircraft.
During flight, the radar module is subjected to an extreme range of
temperatures. The radar module reacts to this thermal cycling by
expanding and contracting in proportion to its coefficient of
thermal expansion. Since the gallium arsenide circuits have a
matching coefficient of thermal expansion they contract and expand
in unison with the radar module. In this manner, the circuits
remain in constant contact with the radar module, thereby ensuring
unbroken electrical connections. Further, since the cubic boron
nitride particles 14 have the second highest thermal conductivity
of any ceramic, they act with the aluminum to transport heat away
from the circuits in an efficient manner. These circuits are also
very low density compared with the copper materials often used.
In another embodiment, particles of cubic boron nitride are mixed
with aluminum particles. The particles are then mixed with a
polymer and injection molded. The system is then sintered in a high
vacuum furnace to consolidate the part.
In another embodiment, the cubic boron nitride particles are coated
with metal and then consolidated.
In another embodiment, the cubic boron nitride particles are mixed
with metal particles and then hot isostatic pressed to consolidate
the part.
Although the invention has been described in detail in the
foregoing embodiments for the purpose of illustration, it is to be
understood that such detail is solely for that purpose and that
variations can be made therein by those skilled in the art without
departing from the spirit and scope of the invention except as it
may be described by the following claims.
* * * * *